AP

Chromosomes

  • T.H. Morgan: first to associated genes with chromosomes
    • worked with Drosphila melanogaster(fruit flies)
  • Fruit flies produce 100s of offspring, new generation every 2 weeks, only 3 autosomal and 1 sex chromosome
  • wild type: the normal/most common phenotype in natural populations
  • mutant: the opposite of wild type
  • sex-linked/X-linked: genes located on sex/X chromosome
  • Y chromosomes has few genes, so most mutants are on the X chromosome
  • genes on the same chromosome passed along as a unit
  • genes on the same chromosome are linked
  • linked genes don’t follow the Law of Independent Assortment
  • Genetic map: an ordered list of loci along a chromosome
  • genetic map was constructed by: Sturtevant, Morgan’s student
  • linkage map: created by associating frequencies of recombinants along the chromosomes
  • the farther apart the two genes, the high the chance that a crossover will occur, and higher the recombination frequency
  • 1 map unit(mu) = 1% chance of recombination
  • more than 50 mu indicates no linkage
  • males determine gender of offspring
  • For a female to express a recessive sex-linked allele, she must be: homozygous recessive
  • hemizygous: only one locus(one X to be expressed)
  • X-linked recessive disorders: re-green color blindness, Duchenne muscular dystrophy, hemophilia
  • X-inactivation: only one of two X chromosomes are active in each cell
  • Barr body: the inactive, condensed X chromosome
  • Where are the Barr body chromosomes reactivated? ovaries
  • Calico cats are only female, only male when: XXY (Klinefelter’s)
  • Nondisjunction: gametes having one extra and one less chromosome
  • Nondisjunction is caused by: error in homolog separation in anaphase I and sister chromatid separation in anaphase II
  • aneuploidy: abnormal chromosome number
  • trisomy: three chromosomes in a gamete
  • monosomy: one chromosome
  • polyploidy: entire extra set of chromosomes; common in plants
  • trisomy 21: down syndrome
  • Klinefelter’s: extra X chromosome
  • Jacob’s syndrome: extra Y chromosome
  • trisomy X: shows no difference from the normal XX
  • Turner’s Syndrome: monosomy X
  • Cri du chat: deletion in chromosome 5
  • Leukemia: reciprocal translocation